def str_reverse(s):
    return s[::-1]  #  --- 将字符串反转后返回

def substr(s,x,y):
    return  s[x:y]  #  ---  将字符串切片

#
# if __name__ == '__main__':
#     print(substr("黑马程序员", 2,4))
#     # print(str_reverse("黑马程序员"))